Summary

Observations have always been essential for humans to understand the Earth system and to thrive. This understanding is critical for harnessing predictability and enabling predictions to inform societally relevant decisions. Better information is needed for understanding the impacts of short-term disruptions, such as extreme weather, flooding, wildland fires, air quality, and volcanic eruptions, and for responding to long-term challenges such as climate change and related impacts to ecosystems, sea level rise, meteorological patterns, and stratospheric ozone. These and other societal imperatives drove the identification of science priorities and observing needs recommended in the most recent (2017) Decadal Survey for Earth Science and Applications from Space (ESAS; NASEM, 2018a). The resulting set of observables has provided clear priorities for space-based measurements, balancing the needs of individual disciplines and providing the foundation to expand interdisciplinary research.

The ESAS study emphasizes the importance of integrating multiple types of observations—from satellites, airborne platforms including piloted aircraft, uncrewed airborne systems (UAS) and balloons, and surface-based platforms—together with modeling, laboratory studies, and analyses to advance knowledge. This integrated approach makes it possible to develop understanding of both long-term trends and episodic events by combining information from instruments that operate at widely ranging spatial and temporal scales. Furthermore, this integration enables studies of the interrelationships among the atmosphere, hydrosphere, cryosphere, ecosystems, and solid earth components of the Earth system.

The National Aeronautics and Space Administration (NASA) and other U.S. science research agencies operate a fleet of research aircraft and other airborne platforms that collectively and collaboratively offer diverse capabilities in range, endurance, payload, altitude range and ceiling, and personnel capacity on board, among other key characteristics. Together, these aircraft can accommodate many instruments across many disciplines and are relevant to addressing the driving questions in Earth system science. Within the fleet, the single Douglas DC-8-72 aircraft (hereafter DC-8) stands out for its unique combination of long endurance, long range, large payload weight and power capacity, flexibility in payload composition, altitude range and ceiling, and space to accommodate many investigators. Acquired in 1987 by NASA, the DC-8 is reaching the end of its useful life and is scheduled to be retired in the 2025 time frame.

At the request of NASA, the National Academies of Sciences, Engineering, and Medicine (the National Academies) established the Committee on Future Use of NASA Airborne Platforms to Advance Earth Science Priorities to provide guidance to the agency about

future needs for a large¹ aircraft and the utility of other airborne platforms for achieving future Earth system science research goals. Specifically, the committee was charged with evaluating whether a large aircraft with capabilities similar to those of the DC-8 is needed to address the priority research and applications questions posed in ESAS. The full Statement of Task is provided in Box S.1.

AIRBORNE SCIENCE NEEDS FOR ADVANCING SCIENCE AND APPLICATIONS PRIORITIES

The ESAS study identified priority research and application areas that span a range of science areas. This report focuses on six areas where airborne platforms are used to undertake research associated with ESAS priority areas and also emphasizes the importance of interdisciplinary research that expands on the integrating themes considered in ESAS. The committee evaluated airborne platform needs to address the science areas, drawing upon input from a community workshop held virtually in July 2020. For each area, the committee considered the role of large and small aircraft, the types of variables to be measured, the contribution of newly available airborne platforms such as UAS and advanced technology balloons, and the support that airborne platforms provide for satellite calibration and validation, computer model testing, instrument development, and workforce training and development.

Key conclusions from this analysis in each of the science areas include:

• Coupling of the water and energy cycles: Advancing understanding of the terrestrial water cycle requires observations collected at multiple spatial and temporal scales, which can be conducted on small, agile aircraft that are able to acquire measurements over a range of altitudes, at different flight speeds, and at multiple times of day. A large aircraft is required for studies of the Earth’s coupled water and energy processes, especially for multi-instrument observations in remote regions.
• Physics and dynamics for improving weather forecasts: To obtain comprehensive sets of measurements covering a wide range of temporal and spatial scales needed for advancement in the weather area, a large aircraft is necessary to meet the requirements for the flight duration, altitude range, and large payload capacity to carry lidars, radars, and in situ onboard and deployable instruments. A large aircraft capable of carrying remote sensors with storm penetration capability (scanning radars) that can target and enable measurements in high-impact weather is also needed, with smaller aircraft and UAS having important supplementary roles.

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¹ For this report, “large” refers to an aircraft like the NASA DC-8, which is defined by a unique combination of endurance, range, payload weight and power capacity, flexibility in payload composition, altitude range and ceiling, and space to accommodate many investigators.

• Air quality and atmospheric chemistry—chemistry coupled to dynamics: Understanding the interplay between future changes in atmospheric composition due to anthropogenic activity and air quality, climate change, and ecosystem dynamics will require a continuation of the airborne science capabilities that the DC-8 has afforded. Small aircraft complement research on a large aircraft or address subsets of atmospheric chemistry but are not an alternative to a large aircraft due to the extremely limited conditions for which formation flying of two or more aircraft with minimal separation can be safely conducted. With new satellite capabilities coming online in the next decade, a strong airborne science capability within the integrated observing system that includes a large aircraft is needed for multi-instrument payloads to measure detailed atmospheric composition.
• Ecosystem change—land and ocean: Future airborne research for ecosystems, including interdisciplinary science, will incorporate multi-instrument, multi-investigator deployments that will require a large aircraft’s heavy lift and size capacity, and some missions will likely require long duration. Research addressing ESAS questions has focused on regional-scale intensive field campaigns and use of several aircraft, each generally carrying a single instrument, which has made it difficult to address ecosystem dependencies and interactions that could be detected using co-located multi-instrument payloads. Instrument incompatibilities resulting from tailoring to individual aircraft are also a challenge for integration on a larger aircraft. Small UAS will have increased applications in the future resulting from instrument miniaturization and increased battery capacity, and mid-size UAS could also be utilized more frequently.
• Sea level rise in a changing climate and coastal impacts: A long-range aircraft is essential for assessing the contributions of Antarctic and Greenland ice sheet melt to sea level rise and has been invaluable in the past for filling data gaps between satellite missions. Heavy-lift capability to complement long-range is not currently essential but has the potential to enable coincident observations from a myriad of instruments, particularly over remote regions around Antarctica and vulnerable coastal areas where impacts of sea level rise will be greatest.
• Surface dynamics, geological hazards, and disasters: Small aircraft have been and will continue to be a key platform type in this area. Coordinated small aircraft are the previously demonstrated and currently preferred approach because they optimize acquisition of synthetic aperture radar (SAR), lidar, and hyperspectral sensors requiring different imaging geometries; they can accommodate a range of weather conditions; and because rapid deployment and frequent temporal sampling are required for disaster responses. The long-range capacity of a large aircraft that could host many sensors (e.g., SAR of

several bands, and/or lidar and optical instruments) could enhance data collection over a long distance and duration, improving efficiency and temporal sampling for interdisciplinary sciences over a large geographic scale.

Many emerging societal needs bridge multiple science areas discussed in this report. For example, landfalling hurricane-induced flooding is a combination of extreme rain, wind, waves, and storm surge, which involves complex interactions of the atmosphere, ocean, coastal environments, and land surface. Similarly, as wildland fire frequency and intensity increase, it is critical to integrate the understanding of fire behavior, atmospheric chemistry, dynamics and circulation in the planetary boundary layer (PBL), and the land surface to facilitate development of new tools for improving fire and air quality forecasts, fire management, and public safety and health. Recognizing the importance of these societal applications areas that cross disciplinary boundaries, the committee also considered the role of airborne observations in advancing this type of interdisciplinary research.

Key conclusions about interdisciplinary science to meet societal needs include the following:

• Advancing understanding, prediction, and decision making on topics spanning many disciplines requires integrated and co-located observations of multiple components of the Earth system. A large aircraft can provide this capability by using integrated multi-instrument payloads and air-deployable devices, such as ocean drifters and floats, dropsondes, and UAS, both to further study of societal applications that are already identified and to have the flexibility for addressing those that will likely emerge in the coming decades.
• Smaller aircraft and UAS are also critical for meeting interdisciplinary, societally relevant needs, particularly when science questions do not require co-located, simultaneous observations—such as mudslides occurring after extreme precipitation on land that has burned or pre- and post-tropical cyclone landfall conditions and flooding—and when aircraft need to be deployed quickly to observe conditions as natural disasters transpire.

THE VALUE OF A LARGE AIRCRAFT IN EARTH SYSTEM SCIENCE RESEARCH

Across the priority science areas, most have identified ESAS questions that can be best addressed using a large aircraft that has the unique DC-8–like combination of long duration, heavy lift, multiple ports, and cruising ability at all altitudes from Earth’s PBL up to about 12.5 km. For many science areas, long-duration capability that enables sampling an event such as tropical cyclones for many hours, or long-range capability that enables sampling over vast oceans and in remote locations such as Antarctica, remain critical.

A Large Aircraft Is Needed for Atmospheric Physics and Dynamics and Atmospheric Chemistry

The committee found a large aircraft to be critical for the areas of physics and dynamics for improving weather forecasts, air quality and atmospheric chemistry—chemistry coupled to dynamics, and the atmospheric component of the coupling of the water and energy cycles. For example, answering questions requiring simultaneous observation of rapidly changing weather conditions with co-located in situ and remote sensing instrumentation is better accomplished with a large aircraft. The same is true for atmospheric chemistry studies in which large numbers of chemical species, aerosol properties, and environmental conditions must be measured simultaneously as the air masses change within seconds while at the same time move rapidly with respect to Earth’s surface. Most airborne atmospheric chemistry research requires essentially all of the capabilities of a large aircraft discussed in this report.

A Large Aircraft Is Needed for Innovative Approaches to Multi-instrument Remote Sensing

Without a large aircraft, the potential is diminished for innovative approaches to integrated research for ecosystem change—land and ocean; surface dynamics, geological hazards, and disasters; and sea level rise in a changing climate and coastal impacts. Potential use of a large aircraft is envisioned to address some key questions in these research areas, especially those that require multisensor measurements or occur in remote regions.

A Large Aircraft Is Needed for Increasingly Interdisciplinary Airborne Research

Earth system science is becoming increasingly interdisciplinary and the committee found potential for a large aircraft to support research questions that advance the science and that will foster expanded and new, innovative investigation across disciplinary boundaries and the interfaces of Earth system components. As questions and collaborations emerge, a large aircraft will provide important flexibility to accommodate and enable new approaches and needs for multi-instrument and air-deployable payloads, and to collect novel combinations of observations simultaneously.

A Large Aircraft Is Needed for Instrument Development

For instrument development, some new instrument concepts for eventual space-based instruments will be able to take advantage of current state-of-the-art technologies and be flown on smaller aircraft, but likely not all. Some will likely be large and heavy, require a large amount of power, be more conservatively designed, and be operated by people on board, thus requiring a large aircraft as a testbed, similar to the Airborne Synthetic Aperture Radar when its technology was state of the art. A large aircraft is essential for testing some future measurement concepts, whether they be multisensor or new discoveries. Having a large aircraft available fosters such innovative thinking, just as it has done for comprehensive airborne studies of global atmospheric composition in

the past. Also, there is a need for new instrument prototypes to be operated on the same airborne platform as the legacy instruments they are replacing so that the performance of the new and legacy instruments can be compared and evaluated. A large aircraft is necessary to accomplish both needs.

A Large Aircraft Is Needed for Satellite Calibration and Validation

The need for a large aircraft for calibration and validation of space-based remote sensing observations will continue to grow. A large aircraft is needed to carry multiple instrument payloads for measuring many atmospheric constituents or properties that calibrate and validate space-based remote sensing observations. The aircraft and payload are needed for vertical profiling under satellite overpasses and over surface-based calibration and validation facilities in widespread locations. Both airborne and space-based observations are used to constrain chemical transport and climate models in addressing Earth system science questions. For satellite remote sensing of surface properties and phenomena, a large aircraft with multisensor payloads is potentially needed for satellite calibration and validation, especially over remote regions. These needs will become more critical in the future as the satellite observations become more complex, requiring more complex satellite calibration and validation strategies.

A Large Aircraft Is Needed for Engaging and Training the Next Generation of Earth System Scientists

Large aircraft will continue to have the benefit of maximizing the number of investigators on board to run instruments and provide opportunities for students and early career scientists to participate in airborne missions. A large aircraft is also an effective facility for attracting, training, and developing a diverse workforce that is critical for embracing rapidly advancing technologies and meeting the challenges of increasing complexity of Earth system science in a changing climate.

A Large Aircraft Is Needed for Providing Capacity to Examine Unexpected Environmental Events

One of the lessons of the past is that we should expect the unexpected to occur in the Earth system. Many of these phenomena have had serious detrimental effects on human health, societies, and economies and need immediate research responses to understand the underlying Earth system science so that sound mitigation strategies can be devised. The Antarctic ozone hole is a prime example of an environmental surprise that was rapidly investigated because the necessary aircraft and instruments were available. Having a large aircraft provides essential capacity in terms of heavy lift and long duration to respond to future unexpected environmental events, thus shortening the time to mitigation.

Recommendation 1: NASA should acquire, maintain, and operate a large aircraft as part of its aircraft fleet in order to address priority questions developed for the 2017 Earth Science and Applications from Space Decadal Survey and to support satellite

calibration and validation, computer model testing, instrument development, and workforce training and development.

The DC-8’s unique combination of characteristics has made it especially valuable for Earth system science research. Addressing future Earth system science needs requires a large aircraft that matches or improves on the DC-8’s capabilities.

Based on past experiences and a vision for future airborne research, the committee here provides a list of essential characteristics and desired minimum values of some characteristics that a new large aircraft should have. The characteristic values are not meant to be prescriptive but rather to serve as guidance for selecting a new large aircraft. The committee recognizes that optimizing combined performance specifications of a new large aircraft may involve performance trade-offs. However, the combination of these characteristics is essential. These specifications are described in Chapter 6 of the report.

• Instrument payload weight of 14,000 kg (30,000 lb) or more
• Flight duration on the order of 12 hours
• Range of 10,000 km (5,400 nmi) or larger
• Altitude ceiling of at least 12.5 km (41,000 ft)
• Extensive vertical profiling capability
• In-flight seating for about 42 or more researchers in addition to crew
• Instrument payload integration and operation flexibility
• Durability
• Precision autopiloting
• In-flight satellite communication links to operations on the ground

This list covers many of the important characteristics that a new large aircraft should have, as identified by the committee, but it is not exhaustive. The new large aircraft should match or improve upon the DC-8 for those characteristics deemed important for accomplishing future Earth system science research goals including those that may not be on this list.

Recommendation 2: To meet NASA objectives, a new large aircraft must have characteristics that are comparable to or better than those of the DC-8 in terms of payload capacity, altitude and distance ranges, instrument sampling port versatility, instrument integration, and durability.

THE BROADER NASA AIRCRAFT FLEET

A new large aircraft is a necessary member of the NASA fleet, but it is only one key contributor to the diverse array of airborne platforms that are needed to address the variety of Earth system science objectives as prioritized in ESAS. Airborne platforms with diverse specifications of payload, range, altitude, onboard pilot, and operational

flexibility form a complementary fleet that can meet a wide range of mission objectives, often in collaboration with airborne platforms in the fleets of other research agencies, private organizations, and other countries. As airborne research evolves and gaps in airborne capability, such as a storm-penetrating aircraft for atmospheric convection research, can be filled, the composition of the entire fleet will likely evolve, as it has in the past, to meet those needs when feasible.

Smaller airborne platforms in the fleet include smaller piloted aircraft as well as UAS and balloons. UAS are being deployed for a wide range of in situ and particularly remote sensing applications. As sensors continue to get smaller and lighter, the role of UAS in Earth system science research will expand dramatically. Large helium-filled balloons are currently the only way to sample the middle stratosphere in situ and, for some stratospheric wind conditions, can stay aloft over a specific region for many days for in situ or remote sensing. In addition, while there are some promising developments in high-altitude, long-duration UAS and in steerable balloons, these technologies may not advance quickly enough to contribute significantly to Earth system science research within the next decade.

A substantial amount of past airborne science research has used more than one airborne platform together in research studies, often deploying different types of aircraft to perform different roles. NASA often contributes its platforms, and the DC-8 in particular as a unique large aircraft, to collaborative efforts that include airborne platforms from other U.S. agencies, other countries, universities, and private organizations. These collaborative efforts will become even more essential as Earth system science questions become more interdisciplinary and more complex. A new large aircraft capability in NASA will continue to play essential and enabling roles in many of these complex, interdisciplinary efforts.

Recommendation 3: NASA should continue operating a diverse array of airborne platforms in addition to a large aircraft, as part of the broader government, university, and commercial fleet, in order to meet the evolving airborne needs for advancing Earth system science research.

PRIORITIZING AND ENABLING INTERDISCIPLINARY EARTH SYSTEM SCIENCE RESEARCH USING A LARGE AIRCRAFT

High-impact weather, climate, and geophysical extreme events are usually the results of complex interactions of various processes either within or among different components of the Earth system and they have large impacts on society, as highlighted by the ESAS integrating themes. The inherent complexity of the Earth system, emerging questions resulting from a foundation of disciplinary knowledge, and rapid Earth system changes being observed today are highlighting the need for growth in interdisciplinary research to meet societal needs. The committee found that primary ESAS questions in all science

areas link to those in other areas, indicating that the need for a large aircraft to carry multi-instrument payloads and air-deployable devices, including UAS, is likely to grow.

Large aircraft can carry suites of instruments necessary to make the simultaneous measurements that will be needed to answer wide-ranging interdisciplinary research questions. It is also possible to imagine benefits of using multiple remote sensing surface measurements from a single large aircraft for research in ecosystem change, high-impact weather and coastal flooding, surface dynamics, and geological hazards in a changing climate and rising seas. Currently, airborne remote sensing of Earth’s surface is accomplished using aircraft smaller than the DC-8 for several reasons: with the miniaturization of remote sensing instruments, a large payload is not needed; incompatible observing requirements for some combinations of remote sensing instruments on a large aircraft have made a combined payload undesirable; the DC-8’s large operating costs exceed available budgets; large, multi-investigator projects in some science areas, such as ecosystems, have not needed the DC-8 during the past 15 years; and the perception that the DC-8 would not be available impeded requests. Scientists will invest time in thinking of innovative strategies involving many measurements from a large aircraft only if they perceive it to be available to them.

By proactively seeking proposals involving innovative approaches for using a large aircraft to accomplish interdisciplinary and surface remote sensing research, in addition to new disciplinary research, NASA will increase the impact that a large aircraft can have on achieving its Earth system science research goals.

Recommendation 4: NASA should continue to solicit large aircraft requests that span the breadth of NASA Earth system science, especially encouraging those for interdisciplinary science across the interfaces of Earth system components with integrated multi-instrument payloads and novel strategies for remote sensing and in situ observations.

LARGE AIRCRAFT FOR TRAINING AND OUTREACH

A large aircraft is an important facility for attracting, training, and developing a diverse workforce and engaging the public because it provides the space to accommodate additional passengers beyond the core scientists and crew needed to carry out the mission.

Attracting young people starts with making them aware of and excited about Earth system science and research opportunities. Taking reporters on research flights and holding public open houses with tours of the aircraft during missions help to generate public knowledge and spark interest in some young children who may not otherwise be attracted to science, technology, engineering, and mathematics (STEM). For undergraduates already studying STEM, programs such as the Student Airborne

Research Program or High Altitude Student Platform engage them in NASA airborne science, encouraging them to pursue careers in Earth system science.

Training graduate students and postdocs on airborne field missions provides them with in-depth knowledge about aspects of Earth system science and associated technical skills, along with other career lessons and benefits. Graduate students and postdocs work closely with each other and more senior scientists as integral members of a team, thus gaining experience and recognition. Missions using large aircraft are particularly effective in this training by exposing early career scientists to the process of in-flight decision making and including them in the onboard discussions of real-time observations from multiple instruments that provide the scientific basis for in-flight decisions.

Creating a more diverse workforce starts with attracting members of underrepresented groups to STEM in K-12 and undergraduate programs and then training and retaining them as they launch their careers. Retention in STEM requires creating equity, inclusion, and a true sense of belonging. While several methods are being implemented by NASA and other organizations to accomplish these goals, some of these methods apply specifically to airborne fieldwork. These methods include training field program participants to adhere to an inclusive code of conduct, enabling participation in fieldwork that is balanced with demands at home, and adjusting approaches to addressing diversity, equity, and inclusion based on information gained from tracking outcomes and creating accountability to meet diversity goals.

Recommendation 5: NASA is encouraged to build on the training and outreach opportunities it has established using the DC-8 and use a future large aircraft to expand its efforts to attract, develop, and train the next-generation workforce, with particular emphasis on diversity, equity, and inclusion, to foster capacity to conduct international Earth system science research, and to inform the public.

Future advancement of NASA airborne Earth system science research depends on a continual emergence of early career scientists to develop new measurement concepts, to make measurements, and to eventually take over field study leadership roles currently held by more senior scientists. A way to ensure the continuity of new talent and their measurement ideas is to continue providing opportunities for early career scientists to participate in NASA airborne science as investigators and to be mentored to become leaders in Earth system science research. Large aircraft such as the DC-8 have been an effective mechanism in NASA airborne science for fostering this mentoring because there is often enough capacity on aircraft deployments to include early career scientists, who sometimes are less experienced and provide unproven new instruments.

Recommendation 6: NASA is encouraged to continue building on its use of the large aircraft capacity to enable scientists with next-generation measurement concepts, especially early career scientists, to become active participants in Earth system science research, even beyond airborne science research.

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